Vitamin B12, which belongs to the B complex of vitamins, is present in a variety of foods, including dairy products, meat and fortified breakfast cereals. Most adults obtain enough vitamin B12 from their diet to meet nutritional requirements. Certain people who have a higher risk of vitamin B12 deficiency, such as people over the age of 50, may need to take vitamin B12 supplements. As a water-soluble vitamin, excess vitamin B12 is usually flushed from the body in urine, and it rarely causes overdose symptoms. However, vitamin B12 may sometimes cause side effects, and thus, you should consult your doctor before taking vitamin B12 supplements.
Allergic Reaction
In rare cases, vitamin B12 can cause an allergic reaction. Vitamin B12 contains cobalt, a metal ion, and people with allergies to cobalt should not take vitamin B12 supplements. Symptoms of a mild allergic reaction include sneezing, coughing, runny nose, nausea and headache. In rare cases, a severe allergic reaction may occur, resulting in rapid swelling of the hands, face, lips and throat, which can potentially close the airways and cause respiratory distress. If you or someone who know experiences severe swelling and difficulty breathing after taking vitamin B12 supplement, you should contact an emergency health care provider immediately.
General Side Effects
At any dose, vitamin B12 supplements have the potential to cause side effects. Skin irritation, including dry, itching skin or rash, has been reported after taking vitamin B12 supplements. Vitamin B12 can also be applied to the skin to treat psoriasis, which may also cause itchy skin as a side effect. Gastrointestinal complaints, such as diarrhea, have also been reported. In certain people, vitamin B12 may increase the risk of blood clots, also known as venous thrombosis.
Disease Interactions
Vitamin B12 supplements have the potential to cause serious complications in people with a rare, hereditary eye disease known as Leber's disease. In people with Leber's disease, vitamin B12 supplements can rapidly cause damage to the eye, causing atrophy of the optic nerve and potentially causing vision loss.
Dosage
The daily recommended dose of vitamin B12 increases with age. Infants less than 6 months old require 0.4 micrograms per day. Adults over the age of 14 require at least 2.4 micrograms per day of vitamin B12 to meet normal nutritional requirements. However, doses up to 1000 micrograms per day have been given to patients to treat diseases, with no increase in the risk of serious side effects.
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